lennyaa[Looking for advice] Searching for a small slim twistable connector
Dave.Some 3:1 glue lined heat shrink on the backs of each connector might do the job.
The glue melts during heating and with a 3:1 ratio you get quite a bit of glue forced in around the wires as it shrinks. It then sets pretty robustly once you get down towards room temperature.
You could try shrinking maybe some 6 or 10mm heatshrink over approx 25-50mm either side of the connector (with a bit of overlap on the connector) and see how it goes. Fully shrunk it’s pretty chunky but it won’t be any bigger than the connector.
I might add, if you can, backfill the connector.
I put silicone epoxy in the back of my JST connections, and adhesive lined shrink.
Those connections are solid.